#include <string.h>
#include <stdint.h>
#include <endian.h>

void *memcpy(void *restrict dest, const void *restrict src, size_t n)
{
    unsigned char *d = dest;
    const unsigned char *s = src;

#ifdef __GNUC__

#if __BYTE_ORDER == __LITTLE_ENDIAN
#define LS >>
#define RS <<
#else
#define LS <<
#define RS >>
#endif

    typedef uint32_t __attribute__((__may_alias__)) u32;
    uint32_t w, x;

    for (; (uintptr_t)s % 4 && n; n--) *d++ = *s++;

    if ((uintptr_t)d % 4 == 0) {
        for (; n>=16; s+=16, d+=16, n-=16) {
            *(u32 *)(d+0) = *(u32 *)(s+0);
            *(u32 *)(d+4) = *(u32 *)(s+4);
            *(u32 *)(d+8) = *(u32 *)(s+8);
            *(u32 *)(d+12) = *(u32 *)(s+12);
        }
        if (n&8) {
            *(u32 *)(d+0) = *(u32 *)(s+0);
            *(u32 *)(d+4) = *(u32 *)(s+4);
            d += 8; s += 8;
        }
        if (n&4) {
            *(u32 *)(d+0) = *(u32 *)(s+0);
            d += 4; s += 4;
        }
        if (n&2) {
            *d++ = *s++; *d++ = *s++;
        }
        if (n&1) {
            *d = *s;
        }
        return dest;
    }

    if (n >= 32) switch ((uintptr_t)d % 4) {
    case 1:
        w = *(u32 *)s;
        *d++ = *s++;
        *d++ = *s++;
        *d++ = *s++;
        n -= 3;
        for (; n>=17; s+=16, d+=16, n-=16) {
            x = *(u32 *)(s+1);
            *(u32 *)(d+0) = (w LS 24) | (x RS 8);
            w = *(u32 *)(s+5);
            *(u32 *)(d+4) = (x LS 24) | (w RS 8);
            x = *(u32 *)(s+9);
            *(u32 *)(d+8) = (w LS 24) | (x RS 8);
            w = *(u32 *)(s+13);
            *(u32 *)(d+12) = (x LS 24) | (w RS 8);
        }
        break;
    case 2:
        w = *(u32 *)s;
        *d++ = *s++;
        *d++ = *s++;
        n -= 2;
        for (; n>=18; s+=16, d+=16, n-=16) {
            x = *(u32 *)(s+2);
            *(u32 *)(d+0) = (w LS 16) | (x RS 16);
            w = *(u32 *)(s+6);
            *(u32 *)(d+4) = (x LS 16) | (w RS 16);
            x = *(u32 *)(s+10);
            *(u32 *)(d+8) = (w LS 16) | (x RS 16);
            w = *(u32 *)(s+14);
            *(u32 *)(d+12) = (x LS 16) | (w RS 16);
        }
        break;
    case 3:
        w = *(u32 *)s;
        *d++ = *s++;
        n -= 1;
        for (; n>=19; s+=16, d+=16, n-=16) {
            x = *(u32 *)(s+3);
            *(u32 *)(d+0) = (w LS 8) | (x RS 24);
            w = *(u32 *)(s+7);
            *(u32 *)(d+4) = (x LS 8) | (w RS 24);
            x = *(u32 *)(s+11);
            *(u32 *)(d+8) = (w LS 8) | (x RS 24);
            w = *(u32 *)(s+15);
            *(u32 *)(d+12) = (x LS 8) | (w RS 24);
        }
        break;
    }
    if (n&16) {
        *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
        *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
        *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
        *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
    }
    if (n&8) {
        *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
        *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
    }
    if (n&4) {
        *d++ = *s++; *d++ = *s++; *d++ = *s++; *d++ = *s++;
    }
    if (n&2) {
        *d++ = *s++; *d++ = *s++;
    }
    if (n&1) {
        *d = *s;
    }
    return dest;
#endif

    for (; n; n--) *d++ = *s++;
    return dest;
}
